Power supply and led lamp device

ABSTRACT

An LED lamp device of the invention includes a power supply unit ( 102, 103 ) supplied with an alternating-current power supply voltage, and an LED lamp ( 106 ) constituted by one or a plurality of serially connected LEDs connected to output terminals of the power supply unit ( 102, 103 ). The power supply unit ( 102 ) obtains a rectified wave of the alternating-current power supply voltage, admits electric power for only part of a time period in which the voltage of the rectified wave corresponding to each half period of the wave of the alternating-current power supply voltage is higher than or equal to a predetermined value, and uses the electric power as power for lighting the LED lamp ( 106 ).

TECHNICAL FIELD

[0001] The present invention relates to a lamp device using LEDs (LightEmitting Diodes) for purposes of indication or illumination, and moreparticularly, to an LED lamp device which can be directly connected(directly coupled) to an alternating-current power supply.

BACKGROUND ART

[0002] Incandescent lamps using a tungsten filament are still popularfor use as various indicator lamps installed in buildings for offices,condominiums, public facilities, etc., such as fire hydrant lamps oremergency lamps, and also as operation button lamps of ticket vendingmachines and other vending machines, elevators, etc. Further, not a fewinterior lighting fixtures still use incandescent lamps depending ontheir purposes.

[0003] With the recent advance of semiconductor device technology, LEDshave come to have performance superior to that of incandescent lamps, interms of the diversity of luminescent color, luminance, durability, andpower consumption (luminous efficacy). Nevertheless, at present LEDs arescarcely used for the aforementioned purposes.

[0004] This is because lamps for indication or illumination purposes areusually put to use on condition that they are directly connected tocommercial alternating-current power supply (100 V in Japan, 110 V inthe United States, 230 V in Europe).

[0005] Namely, as is generally known, an LED operates with several voltsof direct-current (DC) power supply voltage. Thus, in order to useconventional LEDs for the above purposes, it is necessary that a specialpower supply unit be provided to convert the commercialalternating-current power to several volts of DC voltage, but this makesthe LED lamp device expensive and increases the overall size.

[0006] Despite these shortcomings, attempts have conventionally beenmade to connect LEDs directly to the commercial alternating-currentpower supply, as explained below with reference to the drawings.

[0007]FIG. 23 is a circuit diagram showing an LED lamp device ofConventional Type 1.

[0008] In FIG. 23, reference numeral 2003 denotes an AC input terminal H(HOT LINE), 2004 denotes another AC input terminal C (COOL LINE), 2002denotes a full-wave rectifying diode bridge (BrD1), 2005 denotes aseries resistor (Rp), 2006 denotes a constant-current element (CRD:Current Regulated Diode), and 2007 denotes an LED lamp.

[0009] The LED lamp 2007 usually comprises two to eight seriallyconnected LEDs each having a V_(F) value (forward voltage drop) of about2 V, and accordingly, a total V_(F) value is 4 to 16 V. The peak voltageof the fully rectified wave supplied from the diode bridge 2002 isapproximately 140 V in the case of the commercial power supply in Japanwhose root-mean-square value is 100 V.

[0010] Provided that an I_(F) value (forward current) of the LED lampfor attaining the required luminance is about 10 mA and that the LEDlamp is constituted by one LED, the voltage borne by the resistor 2005and the constant-current element 2006 is: 140 V−2 V=138 V, since V_(F)is 2 V, and 138 V×10 mA=1.38 W is consumed by heat dissipation.

[0011] The electric power that contributes to light generation is: 2V×10 mA=0.02 W, and the luminous efficacy is:

0.02 W/(1.38 W+0.02 W)=0.014

[0012] Thus, the luminous efficacy is as low as 1.4%, showing thatnearly 99% of the electric power is lost by heat dissipation.

[0013]FIG. 24 is a circuit diagram showing an LED lamp device ofConventional Type 2.

[0014] In FIG. 24, reference numeral 2105 denotes a voltage regulator(Vreg1), and 2106 denotes a current-limiting resistor (Rc). Also in FIG.24, identical reference numerals are used to denote elements identicalwith or equivalent to those appearing in FIG. 23.

[0015] In Conventional Type 2, variations in voltage of the fullyrectified AC wave are balanced by the voltage regulator 2105; therefore,the constant-current element CRD used in the aforementioned ConventionalType 1 can be omitted and also the light generation is stabilized.However, the efficiency of electric power utilization is basically thesame as (as low as) the aforementioned Conventional Type 1, because ofthe series regulation of voltage.

[0016] As described above, the conventional devices are low inefficiency and high in loss, and thus there has been a demand for adevice improved in these respects.

[0017] An object of the present invention is therefore to provide apower supply unit and an LED lamp device which are high in efficiencyand low in loss.

DISCLOSURE OF THE INVENTION

[0018] To achieve the above object, a power supply unit according to afirst aspect of the invention comprises: rectified wave acquiring meansfor obtaining a rectified wave of an alternating-current power supplyvoltage; and electric power output means for admitting electric powerfor only part of a time period in which a voltage of the rectified waveobtained by the rectified wave acquiring means and corresponding to eachhalf period of a wave of the alternating-current power supply voltage ishigher than or equal to a predetermined value, and for outputting theelectric power as power for driving a load.

[0019] A power supply unit according to a second aspect of the inventioncomprises: a rectifying diode bridge for obtaining a rectified wave of apower supply voltage; an oscillator circuit; a clock signal controlcircuit; and a switched capacitor step-down circuit including aplurality of changeover switches connected in series and capable ofbeing switched between two positions, and a capacitor connected betweenadjacent ones of the changeover switches, wherein the changeoverswitches are switched to either of the two positions by the clock signalcontrol circuit such that the capacitors are charged when the changeoverswitches are in one of the two positions and that the capacitors aredischarged when the changeover switches are in the other of the twopositions, thereby supplying electric power to a load.

[0020] A power supply unit according to a third aspect of the inventionhas two input terminals connected to an alternating-current powersupply, for supplying electric power to a load connected to outputterminals thereof, the power supply unit comprising: an oscillatorcircuit; a clock signal control circuit; a current detection circuit;and two switched capacitor step-down circuits, wherein a highvoltage-side input terminal of one of the two switched capacitorstep-down circuits and a low voltage-side input terminal of the otherswitched capacitor step-down circuit are connected to one of the twoinput terminals of the power supply unit, and a low voltage-side inputterminal of said one switched capacitor step-down circuit and a highvoltage-side input terminal of the other switched capacitor step-downcircuit are connected to the other of the two input terminals of thepower supply unit.

[0021] An LED lamp device according to a fourth aspect of the inventioncomprises: a power supply unit supplied with an alternating-currentpower supply voltage; and an LED lamp including one or a plurality ofserially connected LEDs connected to output terminals of the powersupply unit, wherein the power supply unit obtains a rectified wave ofthe alternating-current power supply voltage, admits electric power foronly part of a time period in which a voltage of the rectified wavecorresponding to each half period of a wave of the alternating-currentpower supply voltage is higher than or equal to a predetermined value,and uses the electric power as power for lighting the LED lamp.

[0022] Preferably, in the LED lamp device according to the fourth aspectof the invention, the power supply unit includes a rectifying diodebridge and a Zener diode serving as a constant-voltage element andconnected in series with the rectifying diode bridge, wherein the diodebridge rectifies the input voltage and then the Zener diode admits theelectric power for only the time period in which the rectified voltageis higher than or equal to the predetermined value, to light the LEDlamp.

[0023] An LED lamp device according to a fifth aspect of the inventioncomprises: a power supply unit supplied with alternating-current ordirect-current power; and an LED lamp including one or a plurality ofserially connected LEDs connected to output terminals of the powersupply unit, wherein a Zener diode is connected in parallel with saidone or plurality of LEDs.

[0024] Preferably, in the LED lamp device according to the fifth aspectof the invention, where the LED lamp comprises a plurality of LED lamps,a constant-current element is connected to the output terminals of thepower supply unit in series with the LED lamps. With this arrangement,even in the event any of the LED lamps burns out and thus turns off, theremaining LED lamps can be kept turned on.

[0025] Also preferably, in the LED lamp device according to the fifthaspect of the invention, the Zener diode has a Zener voltage higher thana forward voltage drop of the LED lamp connected in parallel with theZener diode within a range of from 10% to 30% both inclusive. If thedifference between the Zener voltage and the forward voltage drop issmaller than 10%, dimming cannot be effectively prevented, and if thedifference is greater than 30%, the LED lamp cannot be fully protectedfrom overcurrent.

[0026] An LED lamp device according to a sixth aspect of the inventioncomprises: a power supply unit supplied with an alternating-current ordirect-current power supply voltage; and an LED lamp including one or aplurality of serially connected LEDs connected to output terminals ofthe power supply unit, wherein the power supply unit includes a currentdetection circuit, an input voltage detecting section, an oscillatorcircuit, a switching circuit and a switching element, and the switchingcircuit is supplied with signals from the current detection circuit andthe input voltage detecting section to perform ON/OFF control of theswitching element.

[0027] Preferably, in the LED lamp device according to the sixth aspectof the invention, the power supply unit obtains a rectified wave of thepower supply voltage, admits electric power for only part of a timeperiod in which a voltage of the rectified wave corresponding to eachhalf period of a wave of the alternating-current power supply voltage ishigher than or equal to a predetermined value, and uses the electricpower as power for lighting the LED lamp.

[0028] An LED lamp device according to a seventh aspect of the inventioncomprises: a power supply unit supplied with alternating-current ordirect-current power; and an LED lamp including one or a plurality ofserially connected LEDs connected to output terminals of the powersupply unit, wherein the power supply unit includes an input/outputvoltage detecting section, an oscillator circuit, a switching controlcircuit, a switching element and a current detection circuit, and theswitching control circuit is supplied with signals from the input/outputvoltage detecting section and the current detection circuit to performON/OFF control of the switching element.

[0029] An LED lamp device according to an eighth aspect of the inventioncomprises: a power supply unit supplied with alternating-current ordirect-current power; and an LED lamp including one or a plurality ofserially connected LEDs connected to output terminals of the powersupply unit, wherein the power supply unit includes a rectifying diodebridge, a current detection circuit, an input voltage detecting section,an oscillator circuit, a switching circuit and a switching element, theswitching circuit is supplied with signals from the current detectioncircuit and the input voltage detecting section to perform ON/OFFcontrol of the switching element, and a capacitor is connected betweenthe switching element and the LED lamp such that the capacitor ischarged when the switching element is in an ON state and that electricpower is supplied to the LED lamp from the capacitor when the switchingelement is in an OFF state.

[0030] An LED lamp device according to a ninth aspect of the inventioncomprises: a power supply unit supplied with an alternating-current ordirect-current power supply voltage; and an LED lamp including one or aplurality of serially connected LEDs connected to output terminals ofthe power supply unit, wherein the power supply unit includes arectifying diode bridge for obtaining a rectified wave of the powersupply voltage, an oscillator circuit, a clock signal control circuitand a switched capacitor step-down circuit, the switched capacitorstep-down circuit includes a plurality of changeover switches connectedin series and capable of being switched between two positions, and acapacitor connected between adjacent ones of the changeover switches,and the changeover switches are switched to either of the two positionsby the clock signal control circuit such that the capacitors are chargedwhen the changeover switches are in one of the two positions and thatthe capacitors are discharged when the changeover switches are in theother of the two positions, thereby lighting the LED lamp.

[0031] An LED lamp device according to a tenth aspect of the inventioncomprises: a power supply unit supplied with alternating-current power;and an LED lamp including one or a plurality of serially connected LEDsconnected to output terminals of the power supply unit, wherein thepower supply unit includes an oscillator circuit, a clock signal controlcircuit, a current detection circuit and two switched capacitorstep-down circuits, a high voltage-side input terminal of one of the twoswitched capacitor step-down circuits and a low voltage-side inputterminal of the other switched capacitor step-down circuit are connectedto one of two input terminals of the power supply unit, and a lowvoltage-side input terminal of said one switched capacitor step-downcircuit and a high voltage-side input terminal of the other switchedcapacitor step-down circuit are connected to the other of the two inputterminals of the power supply unit.

[0032] In the aforementioned arrangements according to the invention,the power supply unit is preferably mounted on a flexible printedcircuit board, and the flexible printed circuit board is bent into agenerally S-shaped form. Preferably, moreover, the power supply unit hasterminals attached to opposite sides of the generally S-shaped form ofthe flexible printed circuit board, and has two AC input terminalsattached to opposite surfaces of the flexible printed circuit board.This arrangement makes it possible to save space, to ensure highinsulating performance, and also to improve the characteristics andreliability of the device.

[0033] Also preferably, the power supply unit generates a pulsed currenthaving a peak current value higher than a set average current value, andthe pulsed current has a frequency of not lower than 100 Hz. Thisarrangement makes it possible to increase the luminance perceivable byhuman with the use of less electric power.

[0034] According to the first to fourth and sixth to tenth aspects ofthe invention, the power supply unit is constructed such that electricpower is admitted for only part of a time period of the power supplyvoltage cycle and is output as power for driving a load, thus providinga high-efficiency and low-loss power supply unit capable of driving anLED lamp with the use of a desired voltage higher than the power supplyvoltage, as well as an LED lamp device using such a power supply unit.

[0035] According to the fifth aspect of the invention, a high-efficiencyand low-loss LED lamp device can be provided wherein dimming can beprevented and also the LED lamp can be protected from overcurrent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a circuit diagram showing a device according to a firstembodiment of the present invention;

[0037]FIG. 2 is a diagram illustrating operation of the firstembodiment;

[0038]FIG. 3 is a circuit diagram showing a device according to a secondembodiment of the present invention;

[0039]FIG. 4 is a diagram illustrating operation of the secondembodiment;

[0040]FIG. 5 is a diagram showing in detail an exemplary circuitarrangement of the second embodiment;

[0041]FIG. 6 is a circuit diagram showing a device according to a thirdembodiment of the present invention;

[0042]FIG. 7 is a circuit diagram showing a device according to a fourthembodiment of the present invention;

[0043]FIG. 8 is a diagram illustrating operation of the fourthembodiment;

[0044]FIG. 9 is a diagram showing in detail an exemplary circuitarrangement of the fourth embodiment;

[0045]FIG. 10 is a circuit diagram showing a device according to a fifthembodiment of the present invention;

[0046]FIG. 11 is a diagram illustrating the principle of operation of aswitched capacitor step-down circuit appearing in FIG. 10;

[0047]FIG. 12 is a diagram showing in detail an exemplary circuitarrangement of the switched capacitor step-down circuit;

[0048]FIG. 13 is a circuit diagram showing a device according to a sixthembodiment of the present invention;

[0049]FIG. 14 is a diagram showing in detail an exemplary circuitarrangement of a switched capacitor step-down circuit appearing in FIG.13;

[0050]FIG. 15 shows an exemplary structure of a device according to thepresent invention;

[0051]FIG. 16 is a view showing another exemplary structure of thedevice according to the present invention;

[0052]FIG. 17 shows cross sections of a flexible printed circuit board(Example 1) appearing in FIG. 16, taken along lines shown in the samefigure;

[0053]FIG. 18 similarly shows cross sections of the flexible printedcircuit board (Example 2), taken along the same lines;

[0054]FIG. 19 similarly shows cross sections of the flexible printedcircuit board (Example 3), taken along the same lines;

[0055]FIG. 20 is a circuit diagram showing a device according to aseventh embodiment of the present invention;

[0056]FIG. 21 is a graph showing current-voltage relationships of an LEDlamp and a Zener diode in the seventh embodiment;

[0057]FIG. 22 is a circuit diagram showing a device according to aneighth embodiment of the present invention;

[0058]FIG. 23 is a circuit diagram showing a conventional device (Type1); and

[0059]FIG. 24 is a circuit diagram showing another conventional device(Type 2).

BEST MODE OF CARRYING OUT THE INVENTION

[0060] Embodiments of the present invention will be hereinafterdescribed with reference to the drawings.

[0061]FIG. 1 is a circuit diagram showing a power supply unit and an LEDlamp device according to a first embodiment of the present invention.

[0062] In FIG. 1, reference numeral 102 denotes a full-wave rectifyingdiode bridge (BrD1), 103 denotes a constant-voltage element comprising,in the illustrated example, a Zener diode (Dz1), 104 denotes a seriesresistor (Rp), 105 denotes a constant-current element (Current RegulatedDiode; CRD1), and 106 denotes an LED lamp.

[0063] Reference numeral 108 denotes an AC input terminal H (HOT LINE),and 109 denotes another AC input terminal C (COOL LINE) . The AC inputvoltage is a commercial voltage of 100 V.

[0064] The LED lamp 106 has an anode thereof connected to a positiveoutput terminal of the full-wave rectifying diode bridge 102 via aseries connection of the constant-current element (CRD1) 105, the seriesresistor 104 and the Zener diode 103 with its polarities connected asillustrated, and has a cathode thereof connected directly to a negativeoutput terminal of the diode bridge 102. The LED lamp 106 comprises oneLED or a plurality of serially connected LEDs. The section of thecircuit excepting the LED lamp 106 constitutes a power supply unit (Thisis the case with individual embodiments described later).

[0065] Operation of the first embodiment will be now described withreference also to FIG. 2.

[0066]FIG. 2 shows voltage waveforms appearing at nodes A and Bindicated, respectively, at 107 and 1081 in FIG. 1. In the chart, thevertical axis indicates voltage (V), the horizontal axis indicates time(t), reference numeral 201 denotes the voltage waveform at the node A107, and 202 denotes the voltage waveform at the node B 1081.

[0067] The peak value of the AC input voltage is approximately 140 V,and the Zener diode 103 has a Zener voltage V_(Z) of 100 V.

[0068] As seen from FIG. 2, the AC input voltage of 100 V is subjectedto full-wave rectification by the diode bridge 102, and the Zener diode103 causes the LED lamp 106 to turn on (blink) for a time period inwhich the voltage of the 100-Hz rectified wave is equal to or higherthan 100 V.

[0069] In this case, the ratio of blinking intervals, or morespecifically, the ON-to-OFF duty ratio of the LED lamp 106, is 6:4 (100Hz), and thus the electric power efficiency can be increased (loss canbe reduced) to an extent such that no flickering of light isperceivable.

[0070] The peak value of the voltage applied to the LED lamp 106corresponds to a value by which the peak voltage applied to the LED lamp106, the constant-current element 105 and the series resistor 103exceeds the Zener voltage V_(Z), and therefore, is about 40 V in theillustrated example.

[0071] The current passing through the LED lamp 106 is made constant bythe constant-current element 105.

[0072]FIG. 3 is a circuit diagram showing a power supply unit and an LEDlamp device according to a second embodiment of the present invention.

[0073] In FIG. 3, reference numeral 303 denotes a capacitor (C₁), 304and 305 denote voltage-dividing resistors (R₁, R₂), 306 denotes a powersupply-1 V_(ddH) line, 307 denotes a current detection circuit(I_(DET)), 308 denotes a GND (grounding) line, 309 denotes a zerocrossing detection-type input voltage detection circuit (V_(DET)), 310denotes an oscillator/frequency divider circuit (Osc/Div), 311 to 313denote operating lines, 314 denotes a power supply-2 V_(ddL) line, 315denotes an inductor (coil), 316 denotes a switching element comprisingan n-channel MOSFET, 317 denotes a flywheel diode, and 322 denotes aswitching control circuit (SWCont). In FIG. 3, identical referencenumerals are used to denote elements identical with or equivalent tothose appearing in FIG. 1.

[0074] The resistors 304 and 305, which are connected in series, dividesthe output voltage of the full-wave rectifying diode bridge 102, and avoltage division point thereof is connected to an input terminal of theinput voltage detection circuit 309, an operating power input terminalof the oscillator/frequency divider circuit 310, and the power supply-2V_(ddL) line 314. The capacitor 303 is connected between the voltagedivision point and a ground.

[0075] The series connection of the LED lamp 106, the inductor 315 andthe switching element 316 is connected between the power supply-1V_(ddH) line 306 and the GND line 308, and the current detection circuit307 is inserted in the power supply-1 V_(ddH) line 306. The LED lamp 106comprises, in this case, two to eight LEDs connected in series.

[0076] The flywheel diode 317 is connected in parallel with a seriescircuit constituted by the LED lamp 106 and the inductor 315.

[0077] The switching control circuit 322 is supplied with operatingpower from the power supply-2 V_(ddL) line 314, as well as with signalsfrom the current detection circuit 307, the input voltage detectioncircuit 309 and the oscillator/frequency divider circuit 310, andperforms ON/OFF control of the switching element 316 (LED lamp 106), asdescribed later.

[0078] Operation of the second embodiment will be now described alsowith reference FIG. 4.

[0079]FIG. 4 shows voltage waveforms appearing at nodes A and Bindicated, respectively, at 107 and 321 in FIG. 3. In the figure, thevertical axis indicates voltage (V), the horizontal axis indicates time(t), reference numeral 401 denotes the voltage waveform at the node A107, and 402 denotes the voltage waveform at the node B 321.

[0080] The peak value of the AC input voltage is about 140 V. Theswitching control circuit 322 is so set as to start operation when theinput voltage (voltage at the node A 107) has risen to 40 V from 0 V,and to stop operation when the input voltage has fallen to 40 V from thepeak value. In this example, a voltage at the voltage division pointbetween the resistors 304 and 305 (voltage of the power supply-2 V_(ddL)line 314) is 5 V, and accordingly, the switching control circuit 322outputs an ON voltage of 5 V when in operation.

[0081] As seen from FIG. 4, the AC input voltage of 100 V is subjectedto full-wave rectification by the diode bridge 102, and the switchingcontrol circuit 322 performs ON/OFF control (PWM control) of theswitching element 316 during a time period in which the voltage of therectified wave is higher than or equal to 40 V, so that the LED lamp 106turns on and off (blinks).

[0082] In the illustrated arrangement, the ON/OFF frequency of theswitching element 316, that is, the ON/OFF frequency of the LED lamp106, is 40 kHz, and thus the electric power efficiency can be increased(loss can be reduced) to an extent such that no flickering of light isperceivable.

[0083] The current supplied to the LED lamp 106 is made constant by theswitching control circuit 322 so that constant current can be suppliedto the LED lamp even if the load (the number of LEDs constituting theLED lamp 106) changes.

[0084] The capacitor 303 is applied with the voltage divided by theresistors 304 and 305, in the illustrated example, a low voltage ofabout 5 V. Accordingly, the capacitor to be used may be low in withstandvoltage and also may have a small capacitance since it has only toperform the function of supplying electric power to the input voltagedetection circuit 309, the oscillator/frequency divider circuit 310 andthe switching control circuit 322.

[0085] The “constant current” mentioned above represents a constantcurrent in terms of a mean value. In this embodiment, the switching isperformed by the oscillator circuit; therefore, where the requiredconstant current is 10 mA, for example, the LED lamp is driven with aduty ratio of 30% with the peak current set at 30 mA, thereby obtaininga current of 10 mA on average. The LEDs should desirably be driven bythis method to emit light, for the reason explained below. An LEDexhibits superlinear current-luminance characteristics, rather than justlinear current-luminance characteristics, when the luminance isperceived by human. For example, where the current is doubled, generallythe luminance as perceived is not doubled but is increased by the nthpower of “2” (n is a number equal to or greater than “1”). This isbecause the human eye retains a peak luminance as an afterimage, andprovided that an LED is driven by a DC current having a certain meanvalue and by a duty ratio-controlled (generally, “pulsed”) currenthaving the same mean value but a higher peak value, the human eyeperceives higher brightness when the LED is driven by the pulses thanwhen the LED is driven by the DC current. Thus, by using the pulsedriving technique, an identical perceivable luminance can be attainedwith lower electric power. However, the pulses used should desirablyhave a frequency of not lower than 100 Hz, because if the frequency islower than 100 Hz, a disadvantage arises in that flickering is perceivedby the human eye. The pulse driving technique is similarly effective inthird and fifth embodiments including an oscillator circuit, asdescribed later, and is also effective in fourth and sixth embodimentsinsofar as LEDs are driven by an AC at 100 Hz or above, though theseembodiments include no oscillator circuit.

[0086] In the above embodiment, the power supply-2 V_(dd) is simplifiedin construction through voltage division by means of the resistors, butan active (e.g., switching) power circuit may of course be additionallyprovided (used) so that the operation can advantageously be stabilized.Also, in the foregoing embodiment, the input voltage VDET for startingthe operation is set to 40 V with reference to the input peak voltage of140 V. Where V_(DET) is thus set to be not lower than several tens ofpercent of the input, it is unnecessary to set the ON/OFF ratio (dutyratio), which serves as a switching regulator, to an extremely smallvalue (several percent at the minimum), thus making it easy to provide alarge margin of circuit design. On the other hand, if V_(DET), apartfrom the switching frequency, is excessively increased, an AC frequencyof, for example, 100 Hz manifests itself as flickering, and where theinput AC frequency is 50 Hz or less, for example, the flickering becomesperceivable. In this case, by lowering the input voltage V_(DET) forstarting the operation to 3 to 40 V, the LEDs can be operatedsatisfactorily with an AC frequency of 50 Hz or less, without thepossibility of flickering being perceived. However, the duty ratiopossibly needs to be extremely small (several percent or less at theminimum, producing nearly spike-shaped pulses). The aforementionedmargin of circuit design is in this case relatively narrow, and it istherefore necessary that a high-performance inductor element withexcellent characteristics (DC resistance component) and ahigh-performance switching element with excellent characteristics(switching speed) should be used.

[0087] Thus, elements (devices) with relatively high performance may beused from the outset, V_(DET) is set to 3 to 40 V so that theinconvenience associated with the dynamic range of the duty ratio(generation of spike-shaped pulses at the minimum level) or theflickering due to the AC frequency may not occur, and the operation bymeans of V_(DET) may instead be utilized to stabilize the operations ofthe oscillator circuit and the switching circuit (to perform control ina manner such that the output is provided after the voltage reaches alevel at which the circuits can operate properly), without departingfrom the spirit of the present invention.

[0088]FIG. 5 shows in detail an exemplary circuit arrangement of theaforementioned second embodiment. In FIG. 5, reference numeral 502denotes an integrated circuit which is a one-chip (monolithic) IC. Theswitching element 316 may alternatively be arranged outside theintegrated circuit 502. Also, in FIG. 5, identical reference numeralsare used to denote elements corresponding to those appearing in FIG. 3.

[0089]FIG. 6 is a circuit diagram showing a power supply unit and an LEDlamp device according to a third embodiment of the present invention. InFIG. 6, reference numeral 609 denotes an input/output voltage detectioncircuit, 620 denotes a capacitor (C₂), and 621 denotes a series resistor(Rs). In FIG. 6, identical reference numerals are used to denoteelements identical with or equivalent to those appearing in FIG. 3. Inthis embodiment, however, the switching element 316 comprises a pnptransistor connected in a manner such that the emitter-collector thereofis directed forward to the positive output terminal of the full-waverectifying diode bridge 102, with respect to the LED lamp 106. Also, thecurrent detection circuit 307 is connected to the negative outputterminal of the diode bridge 102.

[0090] The inductor 315 is connected between the switching element 316constituted by the transistor and the LED lamp 106, and the seriesresistor 621 is connected between the inductor 315 and the LED lamp 106.

[0091] The input/output voltage detection circuit 609 detects the outputvoltage, and a detected value of the output voltage is applied to theswitching control circuit 322, like the detected value of the inputvoltage. Specifically, the input/output voltage detection circuit 609functions as a limiter through detection of the output voltage, andcontrols the switching control circuit 322 such that the power supplysection (circuit section excluding the LED lamp 106) usually acts as avoltage feedback switching power supply but acts as a current feedbackswitching power supply when the LED lamp 106 is connected.

[0092] Namely, the input/output voltage detection circuit 609 serves asan output voltage regulator for keeping the output voltage for the LEDlamp at a fixed level. If, in the circuit shown in FIG. 6, the outputvoltage is 16 V and the LED lamp is driven at 2 V, for example, theoutput voltage is set to 2 V when the load exceeds 10 mA. In otherwords, the operation at a constant current of 10 mA is maintained whilethe output voltage is within a range of 2 V to 16 V.

[0093] In the third embodiment, the switching element 316 may beconstituted by an n-channel MOSFET, instead of a pnp transistor.

[0094]FIG. 7 is a circuit diagram showing a power supply unit and an LEDlamp device according to a fourth embodiment of the present invention.

[0095] In FIG. 7, reference numeral 708 denotes a resistor (R₃) for zerocrossing detection, 711 denotes an operating line, 712 denotes an ON/OFFcontrol circuit (ON/OFF Cont), and 716 and 717 denote capacitors (C₃,C₄). Also in FIG. 7, identical reference numerals are used to denoteelements identical with or equivalent to those appearing in FIG. 6. Thecapacitor 716 has the function of smoothing the output voltage of theswitching element 316 (voltage at a node B 715), while the capacitor 717constitutes a discharging/charging circuit in cooperation with theseries resistor 621. In this embodiment, the LED lamp 106 comprises twoto several hundreds of serially connected LEDs.

[0096] Further, the fourth embodiment does not include the currentdetection circuit 307, the oscillator/frequency divider circuit 310, theflywheel diode 317, etc. of the third embodiment shown in FIG. 6, andincludes, instead of the switching control circuit 322, the ON/OFFcontrol circuit 712. The ON/OFF control circuit 712 is supplied with asignal from the input/output voltage detection circuit 609 and performsON/OFF control of the switching element 316, as described below.

[0097] Specifically, in the fourth embodiment, the OFF period of theswitching element 316 is prolonged to further cut down the consumptionof current (electric powder), and during the OFF period, the LED lamp106 is supplied with electric power from the capacitors 716 and 717 tobe turned on.

[0098] Also, in the fourth embodiment, the voltages for turning ON andOFF the switching element 316 can be set by the ON/OFF control circuit712; for example, the ON and OFF voltages may be set to 30 V and 16 V,respectively. Accordingly, a transistor having a low withstand voltagecan be used as the switching element 316.

[0099] Operation of the fourth embodiment will be now described withreference also to FIG. 8.

[0100]FIG. 8 shows voltage waveforms appearing at nodes A and Bindicated, respectively, at 107 and 715 in FIG. 7, wherein the verticalaxis indicates voltage (V), the horizontal axis indicates time (t),reference numeral 801 denotes the voltage waveform at the node A 107,and 802 denotes the voltage waveform at the node B 715.

[0101] The ON/OFF control circuit 712 is applied with the AC inputvoltage having a peak value of approximately 140 V, and operates so asto turn ON the switching element when the input voltage (voltage at thenode A 107) rises to 30 V from 0 V, and to turn OFF the switchingelement while 30 V is exceeded. The voltage at the node B decreasesthereafter, and the switching element remains in the OFF state while thevoltage at the node B decreases from the specified value (about 30 V asstated above) down to 16 V. When the voltage decreases below 16 V, theswitching element is again turned ON. The ON/OFF control circuit 712repeats this operation.

[0102] Thus, in the fourth embodiment, the AC input voltage of 100 V issubjected to full-wave rectification by the diode bridge 102, and theON/OFF control circuit 712 causes the switching element 316 to turn ONduring a time period in which the voltage of the rectified wave is equalto or lower than 30 V and also the output voltage (voltage at the node B715) is below 16 V. The LED lamp 106 is thereafter supplied withelectric power from the capacitors 716 and 717 until the voltage of therectified wave reaches 30 V, whereby the LED lamp can be continuouslylit with low electric power. With this arrangement, the electric powerefficiency can be increased (loss can be reduced), without entailingflickering of light.

[0103] Also, the operation starting and stopping voltages of the ON/OFFcontrol circuit 712 can be set as desired to minimum voltages that arerequired to turn on and off the LED lamp 106 constituted by a desirednumber of serially connected LEDs. Further, the current supplied to theLED lamp 106 can be set as desired by suitably selecting the seriesresistor 621 and the capacitors 716 and 717. Since the lamp can bedriven by a large current, the number of serially connected LEDsconstituting the LED lamp 106 can be increased up to several hundreds.

[0104] The fourth embodiment has been described on the assumption thatthe input used is AC input, for ease of understanding. Needless to say,this embodiment can perform desired operation even if the input used isDC input.

[0105]FIG. 9 shows in detail an exemplary circuit arrangement of thefourth embodiment. In FIG. 9, identical reference numerals denoteelements identical with those appearing in FIG. 7.

[0106]FIG. 10 is a circuit diagram showing a power supply unit and anLED lamp device according to a fifth embodiment of the presentinvention.

[0107] In FIG. 10, reference numeral 1011 denotes an oscillator circuit(Osc), 1013 denotes a clock signal control circuit (CLKCont), 1018denotes a switched capacitor step-down circuit (SCConv), 1021 and 1023denote operating lines, and 1025 denotes a bleeder resistor (R_(B)).Also, in FIG. 10, identical reference numerals are used to denoteelements identical with or equivalent to those appearing in FIGS. 1 and6. In this embodiment, the switched capacitor step-down circuit 1018performs the ON/OFF control of the power supply to the LED lamp 106, aswell as a voltage step-down function and constant-current control.

[0108] The switched capacitor step-down circuit 1018, which is suppliedwith signals from the clock signal control circuit 1013 and the currentdetection circuit 307, controls a positive output (HV) of the full-waverectifying diode bridge 102, applied thereto through theconstant-current element 105, and also provides a direct-current outputDCOUT to the LED lamp 106 to turn on the same.

[0109] Thus, the switched capacitor step-down circuit 1018 has an HVinput terminal 1018 a, an HV output terminal 1018 b, an LV outputterminal 1018 c, a clock input terminal 1018 d, an inverted clock inputterminal 1018 e, and a grounding terminal 1018 f.

[0110] The HV input terminal 1018 a is connected to the positive outputterminal through the constant-current element 105, the HV outputterminal 1018 b is connected to the anode side of the LED lamp 106, andthe LV output terminal 1018 c is connected to the cathode side of theLED lamp 106 through the current detection circuit 307. The clock inputterminal 1018 d and the inverted clock input terminal 1018 e areconnected to a clock output terminal and an inverted clock outputterminal, respectively, of the clock signal control circuit 1013, andthe grounding terminal 1018 f is connected to the GND line 308(grounded).

[0111] The oscillator circuit 1011 is supplied with a voltage divided bythe resistors 304 and 305, and outputs a predetermined oscillatingsignal to the operating line 1023. The clock signal control circuit 1013is supplied with a current detection signal and the oscillating signalvia the operating lines 1021 and 1023, respectively, and provides aclock signal, of which the duty ratio has been controlled in accordancewith the value of the current detection signal, to the switchedcapacitor step-down circuit 1018. The bleeder resistor 1025 is connectedin parallel with the LED lamp 106. The LED lamp 106 comprises two toeight LEDs connected in series.

[0112] The switched capacitor step-down circuit 1018 will be nowdescribed in more detail.

[0113]FIG. 11 illustrates the principle of operation of the switchedcapacitor step-down circuit 1018, wherein SW₁ through SW_(2n) representswitches, and CPT₁ to CPT_(n) represent capacitors. In FIG. 11,reference numerals 1018 a to 1018 f denote the same terminals as thoseshown in FIG. 10.

[0114] The clock input terminal 1018 d is supplied with a clock signalfor shifting the switches SW₁-SW_(2n) individually to “1” side (state1), while the inverted clock input terminal 1018 e is supplied with aninverted clock signal for shifting the switches SW₁-SW_(2n) individuallyto “2” side (state 2).

[0115] The capacitors CPT₁ to CPT_(n) are connected to the switches SW₁to SW_(2n) in a manner such that in the state 1, the capacitors areconnected in series between the HV input terminal 1018 a and thegrounding terminal 1018 f, and that in the state 2, the capacitors areconnected in parallel between the HV output terminal 1018 b and the LVoutput terminal 1018 c. The switches SW₁ to SW_(2n) are connected to therespective terminals 1018 a to 1018 c and 1018 f such that thecapacitors CPT₁ to CPT_(n) can be connected in the above manner in therespective states.

[0116] Referring also to FIG. 10, operation of the switched capacitorstep-down circuit 1018 will be described. In the state 1, the seriallyconnected capacitors CPT₁ to CPT_(n) are connected to the power supply-1V_(ddH) line 306 through the HV input terminal 1018 a, so that currentflows through the capacitors toward the grounding terminal 1018 f,charging the individual capacitors.

[0117] In the state 2, the parallel connected capacitors CPT₁ to CPT_(n)are connected to the anode side of the LED lamp 106 through the HVoutput terminal 1018 b and discharge current flows toward the LV outputterminal 1018 c, so that the LED lamp 106 is turned on.

[0118] The states 1 and 2 alternately take place at a predeterminedfrequency (period) by the action of the switches SW₁ to SW_(2n), thechangeover of which is controlled by the clock signal and the invertedclock signal input to the clock input terminal 1018 d and the invertedclock input terminal 1018 e, respectively. Consequently, theaforementioned charging and discharging of the capacitors CPT₁ toCPT_(n) are repeated at the predetermined frequency to turn on (blink)the LED lamp 106.

[0119] The ON/OFF (blinking) frequency of the LED lamp 106 is set to 40kHz, for example, by the clock signal control circuit 1013, whereby theelectric power efficiency can be increased (loss can be reduced) to anextent such that no flickering of light can be perceived.

[0120] The clock signal control circuit 1013 sets an appropriatefrequency for the clock signal and the inverted clock signal inaccordance with the signal supplied thereto from the current detectioncircuit 307. Also, the output voltage of the switched capacitorstep-down circuit 1018 (HV output terminal 1018 b) is set to a suitablevalue by selecting the capacitance of the capacitors CPT₁ to CPT_(n),etc.

[0121] Thus, with the aforementioned arrangement using the switchedcapacitor step-down circuit 1018, commercial power supply voltage can bedecreased to a low voltage suited for the LED lamp 106 and be applied tothe LED lamp 106, without the need to use a transformer, the inductor315 or a switching element having high withstand voltage. Theconstant-current element 105 may be omitted or replaced by a resistor.

[0122] Specifically, a voltage regulator may be constituted so as toperform voltage feedback control (to output a constant voltage throughalteration of the clock frequency), instead of current feedback control.Thus, this embodiment makes it possible to reduce the size and cost of apower supply for AC adaptors and also is unique and novel because anisolated power supply can be constituted without using a transformer.

[0123]FIG. 12 shows in detail an exemplary circuit arrangement of theswitched capacitor step-down circuit 1018 explained above with referenceto FIG. 11. In FIG. 12, NMOS₁ to NMOS_(3n−1) each represent an n-channelMOSFET. Also, in FIG. 12, identical reference numerals denote elementsidentical with those appearing in FIG. 11.

[0124] The switched capacitor step-down circuit described above is fitto be implemented by a monolithic semiconductor integrated circuit.Specifically, by increasing the number of the serially connectedcapacitors, it is possible to lower the withstand voltage that eachcapacitor should have, and such reduction of the withstand voltagepermits reduction of the thickness of the dielectric film (insulatingfilm), that is, reduction of the area occupied by one capacitor.

[0125]FIG. 13 is a circuit diagram showing a power supply unit and anLED lamp device according to a sixth embodiment of the presentinvention.

[0126] In FIG. 13, reference numeral 105 denotes a constant-currentelement, 106 denotes an LED lamp constituted by two to eight seriallyconnected LEDs, 108 denotes an AC input terminal H, 107 denotes anotherAC input terminal C, and 1025 denotes a bleeder resistor. Also,reference numeral 1300 denotes an integrated circuit which is a one-chip(monolithic) IC, 1301 and 1302 denote switched capacitor step-downcircuits (SCConv), and 1307 and 1308 denote reverse-current blockingdiodes (Di₁, Di₂). The AC input voltage is a commercial power supplyvoltage of 100 V.

[0127] The switched capacitor step-down circuits 1301 and 1302 aresupplied with the AC input from the AC input terminals H 108 and C 107,and provide direct-current outputs DC_(OUT) to the LED lamp 106 to turnon the same.

[0128] Each switched capacitor step-down circuit 1301, 1302 has anAC_(H) input terminal 1301 a, 1302 a, an ACL input terminal 1301 b, 1302b, an HV output terminal 1301 c, 1302 c, and an LV output terminal 1301d, 1302 d.

[0129] The AC_(H) and AC_(L) input terminals 1301 a, 1302 a; 1301 b,1302 b of the switched capacitor step-down circuits 1301 and 1302 areconnected to the AC input terminals in a crosswise fashion.Specifically, the AC_(H) input terminal 1301 a of the switched capacitorstep-down circuit 1301 and the AC_(L) input terminal 1302 b of theswitched capacitor step-down circuit 1302 are connected to the AC inputterminal H 108, while the AC_(L) input terminal 1301 b of the circuit1301 and the AC_(H) input terminal 1302 a of the circuit 1302 areconnected to the AC input terminal C.

[0130] The HV output terminal 1301 c of the switched capacitor step-downcircuit 1301 is connected to the anode side of the LED lamp 106 throughthe reverse-current blocking diode 1307. Similarly, the HV outputterminal 1302 c of the switched capacitor step-down circuit 1302 isconnected to the anode side of the LED lamp through the reverse-currentblocking diode 1308.

[0131] The LV output terminals 1301 d and 1302 d of the switchedcapacitor step-down circuits 1301 and 1302 are joined together andconnected to the cathode side of the LED lamp 106 through theconstant-current element.

[0132] The bleeder resistor 1025 is connected in parallel with the LEDlamp 106, with the constant-current element connected to one endthereof. The LED lamp 106 comprises two to eight serially connectedLEDs.

[0133] The switched capacitor step-down circuits 1301 and 1302 will benow described in more detail.

[0134]FIG. 14 shows in detail an exemplary circuit arrangement of theswitched capacitor step-down circuit 1301, 1302. In FIG. 14, PMOS₁through PMOS_(2n) represent p-channel MOSFETs, CPT₁ through CPT_(n)represent capacitors, and Di_(R1) through Di_(Rn+1) represent rectifyingdiodes. Also, in FIG. 14, reference numerals 1301, 1302, 1301 a to 1301d and 1302 a to 1302 d represent the corresponding elements shown inFIG. 13.

[0135] Each of the p-channel MOSFETs PMOS₁ to PMOS_(2n) is switched OFFwhen positive voltage is applied to the gate thereof, and is switched ONwhen negative voltage is applied to the gate. The capacitors CPT₁ toCPT_(n) are connected to the p-channel MOSFETs PMOS₁ to PMOS_(2n) in amanner such that on the positive side of the AC input, the capacitorsare connected in series between the AC_(H) input terminal 1301 a, 1302 aand the AC_(L) input terminal 1301 b, 1302 b, and that on the negativeside of the AC input, the capacitors are connected in parallel betweenthe HV output terminal 1301 c, 1302 c and the LV output terminal 1301 d,1302 d. The. p-channel MOSFETs PMOS₁ to PMOS_(2n) are connected to theindividual terminals 1301 a to 1301 d, 1302 a to 1302 d so that thecapacitors CPT₁ to CPT_(n) can be connected in the aforementionedmanner.

[0136] Operation of the switched capacitor step-down circuit 1301, 1302will be now described with reference also to FIG. 13. In the case of theswitched capacitor step-down circuit 1301, during the positive intervalof the AC input, the serially connected capacitors CPT₁ to CPT_(n) areconnected to the AC input terminal H 108 through the AC_(H) inputterminal 1301 a, so that current flows through the capacitors toward theAC_(L) input terminal 1301 b, thus charging the capacitors.

[0137] During the negative interval of the AC input, the parallelconnected capacitors CPT₁ to CPT_(n) are connected to the anode side ofthe LED lamp 106 through the HV output terminal 1301 c and thereverse-current blocking diode 1307, and discharge current flows towardthe LV output terminal 1301 d, so that the LED lamp 106 is turned on(blinked) at 50 Hz (in the case where the commercial alternating-currentpower has a frequency of 50 Hz).

[0138] The operation of the switched capacitor step-down circuit 1302 isthe same as that of the above switched capacitor step-down circuit 1301but is reverse thereto with respect to the positive and negativeintervals of the AC input, whereby the LED lamp 106 is turned on(blinked) at 50 Hz (in the case where the commercial alternating-currentpower has a frequency of 50 Hz) with a phase difference of 90° from theswitching operation by the circuit 1301.

[0139] Consequently, the LED lamp 106 is turned on (blinked) at 100 Hz,thus increasing the electric power efficiency (reducing the loss) to anextent such that no flickering of light can be perceived.

[0140] In these switched capacitor step-down circuits 1301 and 1302, thep-channel MOSFETs PMOS₁ to PMOS_(2n) per se are switched on and off(i.e., switched OFF when positive voltage is applied to the gate andswitched ON when negative voltage is applied to the gate), and it istherefore unnecessary to use control pulses (clock etc.). The outputvoltage of each switched capacitor step-down circuit 1301, 1302 (HVoutput terminal 1301 c, 1302 c) is set to a suitable value by selectingthe capacitance of the capacitors CPT₁ to CPT_(n), etc.

[0141] With the aforementioned arrangement using the switched capacitorstep-down circuits 1301 and 1302, the commercial power supply voltagecan be lowered to a voltage suited for the LED lamp 106 and be appliedto the lamp, without the need to use a transformer, the inductor 315 ora switching element with high withstand voltage. Also, this embodimentmakes it unnecessary to use the full-wave rectifying diode bridge.

[0142] Namely, a voltage regulator is constituted so as to performvoltage feedback control (to output a constant voltage), instead ofcurrent feedback control. Thus, like the fifth embodiment, thisembodiment makes it possible to reduce the size and cost of a powersupply for AC adaptors and also is unique and novel because an isolatedpower supply can be constituted without using a transformer.

[0143] In the sixth embodiment (FIG. 13), the constant-current element105 may alternatively be connected to the anode side of the LED lamp106, and the reverse-current blocking diodes 1307 and 1308 may beomitted. Further, the bleeder resistor 1025 and the constant-currentelement 105 may be provided outside the integrated circuit 1300 (asexternal elements).

[0144]FIG. 15 shows an exemplary structure of an LED lamp deviceaccording to the present invention, wherein (a) is a front view, (b) isa rear view, (c) is a right side view, and (d) is a sectional view takenalong line D-D in (c). It is to be noted that the figures illustrate aminimum structure.

[0145] In the figures, reference numeral 1501 denotes an E-10 type base,1502 denotes a cylindrical case of synthetic resin or glass coupled tothe base 1501, and 1503 denotes an LED lamp module so attached as toclose a distal end of the case 1502. The lamp device is formed so thatits external shape as a whole may resemble that of a glow starter forfluorescent lamps having an E-10 type base.

[0146] The LED lamp module 1503 has eight LED chips 1503 a arranged in amanner such that, as shown in the front view, the LED chips are situatedon an identical concentric circle with an appropriate radius from thecenter of the module 1503 at nearly equal intervals in thecircumferential direction. The LED chips 1503 a, which are connected inseries, are connected to the output terminal of a power supply unit 1504(the circuit section excluding the LED lamp 106 in the aforementionedindividual embodiments).

[0147] The power supply unit 1504 includes a full-wave rectifying diodebridge 1504 a, an IC chip 1504 b, an inductor 1504 c, and a circuitboard 1504 d on which these elements 1504 a to 1504 c are mounted (inthe case of the second to fourth embodiments). In the case of the first,fifth and sixth embodiments, the inductor 1504 c is omitted.

[0148] Reference numerals 1504 e and 1504 f denote AC input lead wires,and 1504 g and 1504 h denote power supply lead wires for the LED lampmodule.

[0149] With the device of the present invention constructed as describedabove, the base 1501 is screwed into a commercial alternating-currentpower input socket (not shown), whereupon the commercialalternating-current power is supplied to the power supply unit 1504through the AC input lead wires 1504 e and 1504 f and the eight LEDchips 1503 a in the LED lamp module 1503 are turned on simultaneouslyfor the purpose of indication or illumination.

[0150]FIG. 16 is a sectional view showing another exemplary structure ofthe LED lamp device according to the present invention, wherein thepower supply unit 1504 of the aforementioned individual embodiments,excepting the LED lamp 106, is mounted on a flexible printed circuitboard 1601.

[0151]FIG. 17 shows sections of the flexible printed circuit board 1601taken along lines I-I, II-II and III-III in FIG. 16, respectively.

[0152] In FIGS. 16 and 17, reference numerals 1604 a and 1604 b denoteAC input terminals, and 1604 c and 1604 d denote power supply terminalsfor the LED lamp module. Also, in FIG. 16, identical reference numeralsare used to denote elements identical with or equivalent to thoseappearing in FIG. 15.

[0153] As seen from the figures, the flexible printed circuit board1601, which is used as the circuit board, is bent into an S- or Z-shapeas viewed in cross section (in the illustrated example, S-shape),thereby saving space and making it unnecessary to use jumper wires.

[0154] The AC input terminals 1604 a and 1604 b and the LED lamp modulepower supply terminals 1604 c and 1604 d (solder lands or pads on theboard 1601) are positioned as illustrated in FIG. 17. The terminals mayalternatively be positioned as shown in FIG. 18 or 19.

[0155] Specifically, the power supply terminals 1604 c and 1604 d forthe LED lamp module 1503 are positioned close to the LED lamp module andat the same time are mounted on the opposite surfaces of the board 1601,as illustrated. Also, as shown in FIGS. 17 to 19, the AC input terminals1604 b and 1604 a are arranged on the opposite surfaces of the board1601 but at a distance from each other (above and below in the figures)in the longitudinal direction of the case 1502.

[0156] With this arrangement, a large creeping distance can be securedbetween the terminals 1604 a, 1604 b, 1604 c and 1604 d, especiallybetween the AC input terminals 1604 a and 1604 b to which high voltageis applied, thus making it possible to ensure high insulatingperformance and also to improve the characteristics and reliability ofthe device.

[0157] In the first to third and fifth embodiments among the foregoingembodiments, DC input may be used in place of AC input, and also in thiscase the LED lamp 106 can be turned on.

[0158] Referring now to FIGS. 20 and 21, a seventh embodiment will bedescribed. In the circuit diagram of FIG. 20 and the circuit diagram ofFIG. 22 showing an eighth embodiment described later, identicalreference numerals are used to denote elements identical with those ofthe first embodiment, and description of such elements is omitted.

[0159] As shown in FIG. 20, in the seventh embodiment, theconstant-current element 105 and the LED lamp 106, which are connectedin series, are connected to the full-wave rectifying diode bridge 102which is connected between the AC input terminals 108 and 107, and aZener diode 2001 is connected in parallel with the LED lamp 106.

[0160] In the seventh embodiment, while the voltage applied to the LED106 is lower than a predetermined voltage V_(F), current flows throughthe Zener diode 2001, so that the LED 106 is prevented from being litdimly. Also, overcurrent is turned aside to the Zener diode 2001 andthus is prevented from flowing to the LED 106, whereby the LED 106 canbe protected from such overcurrent.

[0161] Specifically, as seen from the current I-voltage V relationshipof the LED lamp 106 and the Zener diode 2001 shown in FIG. 21, in aregion S in which the voltage is lower than the forward voltage dropV_(F) of the LED lamp 106, the LED lamp 106 normally does not turn on.Because of high impedance, however, a current of small amperage (e.g.,100 to 500 μA) can flow through the circuit even when the switches ofthe AC input terminals 108 and 107 are disconnected (OFF). Since suchcurrent is allowed to leak through the Zener diode 2001 in the constantcurrent region S and does not flow through the LED lamp 106, the lamp isprevented from being lit dimly. In a voltage range W (e.g., from 2 V to3 V) in which the voltage is higher than V_(F) of the LED 106 and thecurrent I is in the vicinity of 10 mA, the LED 106 turns on. If thecurrent I exceeds the range W, such overcurrent flows through the Zenerdiode 2001. Thus, the LED 106 can be prevented from being lit dimly andalso can be protected from overcurrent.

[0162] In the seventh embodiment, the Zener voltage of the Zener diode2001 should preferably be higher than V_(F) (forward voltage drop) ofthe LED lamp connected in parallel with the Zener diode within a rangeof from 10% to 30% both inclusive. If the difference between the Zenervoltage and V_(F) is smaller than 10%, dimming cannot be effectivelyprevented, and if the difference is greater than 30%, the LED lamp 106cannot be fully protected from overcurrent.

[0163]FIG. 22 illustrates an eighth embodiment. In the eighthembodiment, a plurality of LED lamps 106 (each may be a unit includingmultiple LED chips) are connected in series, and a Zener diode 2001 isconnected in parallel with each of the LED lamps 106. With thearrangement of the eighth embodiment, even if any of the LED lamps 106burns out and thus turns off (circuit opens), current flows through theZener diode 2001 connected in parallel with the burned-out lamp 106while causing breakdown of the Zener diode, because of the provision ofthe constant-current element 105, so that the remaining LED lamps 106can be kept turned on.

[0164] In other words, although the LED lamps 106 are connected inseries, an advantage similar to that obtained in the case of theparallel connection of lamps can be achieved. Moreover, needless to say,the total electric power required for the series connection of the LEDlamps 106 is smaller than in the case of the parallel connection of thelamps.

INDUSTRIAL APPLICABILITY

[0165] As seen from the above description, the present invention isuseful as a device for indication or illumination, such as indicatorlamps, fire hydrant lamps, emergency lamps, operation button lamps ofticket vending machines and other vending machines, elevators, etc., andalso as a power supply unit for such lamps.

1. A power supply unit characterized by comprising: rectified waveacquiring means for obtaining a rectified wave of an alternating-currentpower supply voltage; and electric power output means for admittingelectric power for only part of a time period in which a voltage of therectified wave obtained by said rectified wave acquiring means andcorresponding to each half period of a wave of the alternating-currentpower supply voltage is higher than or equal to a predetermined value,and for outputting the electric power as power for driving a load.
 2. Apower supply unit characterized by comprising: a rectifying diode bridgefor obtaining a rectified wave of a power supply voltage; an oscillatorcircuit; a clock signal control circuit; and a switched capacitorstep-down circuit including a plurality of changeover switches connectedin series and capable of being switched between two positions, and acapacitor connected between adjacent ones of the changeover switches,the changeover switches being switched to either of the two positions bysaid clock signal control circuit such that the capacitors are chargedwhen the changeover switches are in one of the two positions and thatthe capacitors are discharged when the changeover switches are in theother of the two positions, thereby supplying electric power to a load.3. A power supply unit having two input terminals connected to analternating-current power supply, for supplying electric power to a loadconnected to output terminals thereof, characterized by comprising: anoscillator circuit; a clock signal control circuit; and two switchedcapacitor step-down circuits, a high voltage-side input terminal of oneof the two switched capacitor step-down circuits and a low voltage-sideinput terminal of the other switched capacitor step-down circuit beingconnected to one of the two input terminals of said power supply unit, alow voltage-side input terminal of said one switched capacitor step-downcircuit and a high voltage-side input terminal of said other switchedcapacitor,step-down circuit being connected to the other of the twoinput terminals of said power supply unit.
 4. An LED lamp devicecharacterized by comprising: a power supply unit supplied with analternating-current power supply voltage; and an LED lamp including oneor a plurality of serially connected LEDs connected to output terminalsof said power supply unit, wherein said power supply unit obtains arectified wave of the alternating-current power supply voltage, admitselectric power for only part of a time period in which a voltage of therectified wave corresponding to each half period of a wave of thealternating-current power supply voltage is higher than or equal to apredetermined value, and uses the electric power as power for lightingsaid LED lamp.
 5. The LED lamp device according to claim 4,characterized in that said power supply unit includes a rectifying diodebridge and a Zener diode serving as a constant-voltage element andconnected in series with the rectifying diode bridge, the diode bridgerectifying the input voltage and then the Zener diode admitting theelectric power for only the time period in which the rectified voltageis higher than or equal to the predetermined value, to light said LEDlamp.
 6. An LED lamp device characterized by comprising: a power supplyunit supplied with alternating-current or direct-current power; and anLED lamp including one or a plurality of serially connected LEDsconnected to output terminals of said power supply unit, wherein a Zenerdiode is connected in parallel with said one or plurality of LEDs. 7.The LED lamp device according to claim 6, characterized in that said LEDlamp comprises a plurality of LED lamps, a constant-current elementbeing connected to the output terminals of said power supply unit inseries with said plurality of LED lamps.
 8. The LED lamp deviceaccording to claim 7, characterized in that said Zener diode has a Zenervoltage higher than a forward voltage drop of the LED lamp connected inparallel with said Zener diode within a range of from 10% to 30% bothinclusive.
 9. An LED lamp device characterized by comprising: a powersupply unit supplied with an alternating-current or direct-current powersupply voltage; and an LED lamp including one or a plurality of seriallyconnected LEDs connected to output terminals of said power supply unit,wherein said power supply unit includes a current detection circuit, aninput voltage detecting section, an oscillator circuit, a switchingcircuit, and a switching element, the switching circuit being suppliedwith signals from the current detection circuit and the input voltagedetecting section to perform ON/OFF control of the switching element.10. The LED lamp device according to claim 9, characterized in that saidpower supply unit obtains a rectified wave of the power supply voltage,admits electric power for only part of a time period in which a voltageof the rectified wave corresponding to each half period of a wave of thealternating-current power supply voltage is higher than or equal to apredetermined value, and uses the electric power as power for lightingsaid LED lamp.
 11. An LED lamp device characterized by comprising: apower supply unit supplied with alternating-current or direct-currentpower; and an LED lamp including one or a plurality of seriallyconnected LEDs connected to output terminals of said power supply unit,wherein said power supply unit includes an input/output voltagedetecting section, an oscillator circuit, a switching control circuit, aswitching element, and a current detection circuit, the switchingcontrol circuit being supplied with signals from the input/outputvoltage detecting section and the current detection circuit to performON/OFF control of the switching element.
 12. An LED lamp devicecharacterized by comprising: a power supply unit supplied withalternating-current or direct-current power; and an LED lamp includingone or a plurality of serially connected LEDs connected to outputterminals of said power supply unit, wherein said power supply unitincludes a rectifying diode bridge, a current detection circuit, aninput voltage detecting section, an oscillator circuit, a switchingcircuit, and a switching element, the switching circuit being suppliedwith signals from the current detection circuit and the input voltagedetecting section to perform ON/OFF control of the switching element, acapacitor being connected between the switching element and the LED lampsuch that the capacitor is charged when the switching element is in anON state and that electric power is supplied to the LED lamp from thecapacitor when the switching element is in an OFF state.
 13. An LED lampdevice characterized by comprising: a power supply unit supplied with analternating-current or direct-current power supply voltage; and an LEDlamp including one or a plurality of serially connected LEDs connectedto output terminals of said power supply unit, wherein said power supplyunit includes a rectifying diode bridge for obtaining a rectified waveof the power supply voltage, an oscillator circuit, a clock signalcontrol circuit, and a switched capacitor step-down circuit, theswitched capacitor step-down circuit including a plurality of changeoverswitches connected in series and capable of being switched between twopositions, and a capacitor connected between adjacent ones of thechangeover switches, the changeover switches being switched to either ofthe two positions by the clock signal control circuit such that thecapacitors are charged when the changeover switches are in one of thetwo positions and that the capacitors are discharged when the changeoverswitches are in the other of the two positions, thereby lighting saidLED lamp.
 14. An LED lamp device characterized by comprising: a powersupply unit supplied with alternating-current power; and an LED lampincluding one or a plurality of serially connected LEDs connected tooutput terminals of said power supply unit, wherein said power supplyunit includes an oscillator circuit, a clock signal control circuit, acurrent detection circuit, and two switched capacitor step-downcircuits, a high voltage-side input terminal of one of the two switchedcapacitor step-down circuits and a low voltage-side input terminal ofthe other switched capacitor step-down circuit being connected to one oftwo input terminals of said power supply unit, a low voltage-side inputterminal of said one switched capacitor step-down circuit and a highvoltage-side input terminal of said other switched capacitor step-downcircuit being connected to the other of the two input terminals of saidpower supply unit.
 15. The LED lamp device according to any one ofclaims 4 through 14, characterized in that said power supply unit ismounted on a flexible printed circuit board, the flexible printedcircuit board being bent into a generally S-shaped form.
 16. The LEDlamp device according to claim 15, characterized in that said powersupply unit has terminals attached to opposite sides of the generallyS-shaped form of the flexible printed circuit board, and has two ACinput terminals attached to opposite surfaces of the flexible printedcircuit board.
 17. The LED lamp device according to any one of claims 4through 16, characterized in that said power supply unit generates apulsed current having a peak current value higher than a set averagecurrent value, the pulsed current having a frequency of not lower than100 Hz.
 18. The power supply unit according to any one of claims 1 to 3,characterized in that said power supply unit is mounted on a flexibleprinted circuit board, the flexible printed circuit board being bentinto a generally S-shaped form.
 19. The power supply unit according toclaim 18, characterized in that said power supply unit has terminalsattached to opposite sides of the generally S-shaped form of theflexible printed circuit board, and has two AC input terminals attachedto opposite surfaces of the flexible printed circuit board.
 20. Thepower supply unit according to any one of claims 1 to 3, characterizedin that said power supply unit generates a pulsed current having a peakcurrent value higher than a set average current value, the pulsedcurrent having a frequency of not lower than 100 Hz.